Differential Diagnosis

• Single most likely diagnosis
  • Infectious mononucleosis: This diagnosis is the most likely due to the patient's symptoms, including sore throat, weakness, fever, and lymphadenopathy (enlarged lymph nodes), which are all characteristic of infectious mononucleosis. The absence of plaque on the tonsils and the presence of lymphadenopathy in multiple regions also support this diagnosis.
• Other Likely diagnoses
  • HIV infection: Given the patient's sexual partner has been using drugs irregularly for 2 years, there's an increased risk of HIV transmission. The symptoms of acute HIV infection can include fever, sore throat, and lymphadenopathy, making it a plausible diagnosis.
  • Adenovirus infection: Adenovirus can cause a range of symptoms including fever, sore throat, and lymphadenopathy, although it's less commonly associated with significant lymph node enlargement compared to infectious mononucleosis.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Lymphoma: Although less likely given the acute presentation, lymphoma can present with lymphadenopathy and systemic symptoms like fever and weakness. Missing this diagnosis could have severe consequences, making it crucial to consider.
• Rare diagnoses
  • Angina: While angina (as in tonsillitis) could explain the sore throat, it typically doesn't account for the widespread lymphadenopathy or the systemic symptoms like weakness and fever to the extent seen in this patient.
  • Other rare infections or conditions could also be considered but are less likely given the information provided.